1. Field of the Invention
This invention relates to a process for producing 2,6-dichloro-3-nitropyridine by an improved nitration process of 2,6-dichloropyridine.
2. Description of the Prior Art
It has been reported that 2,6-dichloro-3-nitropyridine has useful herbicidal properties. Furthermore, this compound is useful as a chemical intermediate for dyes, pharmaceutical and other agricultural applications.
It is known that 2,6-dichloropyridine could be nitrated with a mixture of HNO.sub.3 and H.sub.2 SO.sub.4 to give 2,6-dichloro-3-nitropyridine. See Johnson et al, J. Chem. Soc. (B), 1967, pp. 1204-1210 and U.S. Pat. No. 3,809,695, issued to Steinmetz et al on May 7, 1974. However, the nitration reactions disclosed by these prior art references employed relatively high molar ratios of HNO.sub.3 to 2,6-dichloropyridines (i.e., both were over 10:1) to effect the nitration. Also, these inventions were accompanied by the evolution of hazardous brown nitrogen oxides from the reaction mixture. On large commercial scale operations, the employment of this relatively high molar ratio and evolution of hazardous fumes are both undesirable because of the low productivity associated with the high levels of HNO.sub.3 needed and possible environment problems, respectively.
Accordingly, it would be beneficial if the conditions of this nitration reaction could be improved so that lower molar ratios of HNO.sub.3 to 2,6-dichloropyridine could be employed and little or no evolution of nitrogen oxides occurred during the reaction.